Polishing of anaerobic secondary effluent by Chlorella vulgaris under low light intensity

Abstract To investigate anaerobic secondary effluent polishing by microalgae ( Chlorella vulgaris ) under low light intensity (14 μmol/m 2 /s), bubbling column reactors were operated in batches of 8 d with initial ammonium nitrogen 10–50 mg/L, initial phosphate phosphorus 2–10 mg/L and microalgal seed 40 mg/L. Maximum microalgal biomass and minimum generation time were 370.9 mg/L and 2.5 d, respectively. Nitrogen removal (maximum 99.6%) was mainly attributed to microalgal growth rate, while phosphorus removal (maximum 49.8%) was related to microalgal growth rate, cell phosphorus content (maximum 1.5%) and initial nutrients ratio. Dissolved microalgal organics release in terms of chemical oxygen demand (maximum 63.2 mg/L) and hexane extractable material (i.e., oil and grease, maximum 8.5 mg/L) was firstly reported and mainly affected by nitrogen deficiency and deteriorated effluent quality. Ultrafiltration critical flux (16.6–39.5 L/m 2 /h) showed negative linear correlation to microalgal biomass. Anaerobic membrane bioreactor effluent polishing showed similar results with slight inhibition to synthetic effluent.